In addition to subcutaneous injection, I've found that ozone therapy can/has been administered by:

*rectal insufflation (blowing it up and into the rectum)
*vaginal insufflation (ditto for the vagina)
*withdrawing 6 to 12 oz. of blood, putting it into an ozone-containing container, shaking it to mix the ozone and the blood, and replacing the blood in the patient.

I'm no physician but it seems to me that each of these methods has definite risks.

Oh, yes -- ozone has been used "topically" on skin infections. This seems to me that, used with care, it might be safe.